Hepatocyte-dependent cross-presentation of soluble antigens induces antigen-specific CD8(+) T cell tolerance

The ability of hepatocytes to cross-present soluble extracellular antigens and the related immunological outcomes remain poorly investigated. Our work shows that murine primary hepatocytes actively uptake and process extracellular antigens in EEA1 + and TAP1 + phagosomes, which are functionally related to cross-presentation. In fact EEA1 + TAP1 + organelles, which are one of the signatures of professional cross-presenting cells, are also found in the cytoplasm of hepatocytes. Moreover, in vitro hepatocyte-dependent cross-presentation of OVA to OT-I cells is sensitive to specific drug inhibitors of endosomal and proteasomal activity, providing direct evidence that endocytosed antigens enter the cross-presentation pathway. In vivo , cross-presenting hepatocytes induce tolerance of adoptively transferred OT-I cells by clonal deletion, as pro-apoptotic markers are upregulated on hepatocyte-educated OT-I cells. Non-deleted OT-I cells show instead significantly reduced response to vaccination, indicative of anergy. Active engulfment or emperipolesis of antigen cross-presenting hepatocytes by OT-I cells is also detected in vitro , as an additional means of T cell deletion. PD-1/PD-L1 interactions participate in the induction of hepatocyte-dependent cross-tolerance, as specific blockage of PD-L1 on hepatocytes significantly reduces the development of hepatocyte-dependent cross-tolerance. Due to their physiologic metabolic functions and their capacity to cross-present extracellular antigens here described, we propose hepatocytes as one of the major players in the establishment of antigen-specific CD8 + T cell peripheral tolerance.